In general, the invention relates to hydraulic systems used in the operation of heavy equipment. More specifically, the invention relates to a electrohydraulic or hydraulic system used for regulating pressure equalization to alleviate harsh oscillation common in the operation of heavy equipment, including but not limited to backhoes, excavators, skid steer drives, crawler drives, outriggers, and wheel loaders.
In general, construction and other heavy equipment use hydraulic systems to perform digging, loading, craning, and like operations. The speed and direction of these functions are controlled with hydraulic valves. Typically at the end of a moving function, the assembly exhibits uncontrolled changes in speed and direction producing an oscillatory motion. For example, in a backhoe, the oscillatory motion occurs when its linkage is brought to a stop following a side-to-side maneuver. This oscillation makes it more difficult for the backhoe operator to return the bucket to a given position. The oscillation is caused when the kinetic energy generated by the backhoe movement is transferred to the hydraulic supply lines connected to the backhoes actuators when stopping. The transferred energy produces a sharp increase (or spike) in fluid pressure in the stopping actuator. The increased fluid pressure transfers the energy into the hydraulic system and the surrounding vehicle. The energy then returns in the opposite direction through the hydraulic lines and exerts the force into the original driving actuator. This transfer of energy continues until it is dispelled as heat, or is dissipated through the oscillation of the equipment and the swelling of the hydraulic lines.
Thus, there is a need in the hydraulic system for an additional system that reduces the amount of oscillatory motion that occurs when a swinging backhoe or other heavy machinery component is brought to a stop. Further, there is a need for increasing the accuracy when swinging the backhoe or other heavy machinery linkage to a desired location.
In accordance with a first embodiment of the invention, a hydraulic system for suppressing oscillation in a linkage of heavy equipment is provided that includes first and second hydraulic conduits, a crossover valve in communication with the first and second hydraulic conduits to control the flow of hydraulic fluid between the first and second conduits, and a hydraulic control circuit in communication with the valve and configured to open the valve in response to the deceleration of the heavy equipment. The system may include at least one dual-ported hydraulic cylinder coupled to the linkage to move the linkage and further wherein the hydraulic control circuit is responsive to a flow of fluid ejected from the cylinder by conversion of kinetic energy of the linkage. The valve may be configured to open in response to the flow of fluid ejected from the cylinder by conversion of kinetic energy of the linkage. The valve, once opened, may be configured to remain open for a predetermined period of time after stoppage of the flow of fluid ejected from the cylinder by conversion of kinetic energy of the linkage. The hydraulic control circuit may include a first hydraulic signal line coupled to the valve to apply a closing force to the valve and a second hydraulic signal line coupled to the valve to apply an opening force to the valve. The fluid pressure applied to the first signal line may tend to close the valve and fluid pressure applied to the second hydraulic signal line may tend to open the valve. The first hydraulic signal line may be fluidly coupled to the first conduit when the fluid pressure in the first conduit is greater than the fluid pressure in the second conduit and may be also fluidly coupled to the second conduit when the fluid pressure in the second conduit is greater than the fluid pressure in the first conduit. The second hydraulic signal line may be fluidly coupled to the first conduit when the fluid pressure in first conduit is greater than the fluid pressure in the second conduit and may be also fluidly coupled to the second conduit when the fluid pressure in second conduit is greater than the fluid pressure in the first conduit. The first hydraulic signal line may be configured to prevent hydraulic fluid that has entered the first hydraulic signal line from returning to the first and second conduits. The first hydraulic signal line may include at least one check valve configured to prevent fluid in the first hydraulic line from returning to the first and second conduits. The valve may be configured (1) to open in response to a flow of fluid in the first conduit that is ejected from the cylinder by conversion of kinetic energy of the linkage, and (2) to open in response to a flow of fluid in the second conduit that is ejected from the cylinder by conversion of kinetic energy of the linkage. The system may include a first flow restriction device fluidly coupled to the first conduit between a first and a second portion of the first conduit to provide a first pressure drop in response to fluid flow in a first direction through the first conduit. The hydraulic control circuit may include a first hydraulic signal line fluidly coupled to and between the valve and the first portion of the first conduit and configured to apply a closing force to the valve, and a second hydraulic signal line fluidly coupled to and between the valve and the second portion of the first conduit and configured to apply an opening force to the valve. Fluid pressure applied to the first signal line may tend to close the valve and fluid pressure applied to the second hydraulic signal line may tend to open the valve. The system may include a second flow restriction device fluidly coupled to the second conduit between a first and a second portion of the second conduit to provide a second pressure drop in response to fluid flow in a first direction through the second conduit. The system may include a third flow restriction device fluidly coupled to the first conduit between the first and the second portion of the first conduit to provide a second pressure drop in response to fluid flow through the first conduit in a second direction opposite the first direction. The first pressure drop and the second pressure drop may be different. The first pressure drop may be less that the second pressure drop. The valve may be configured (1) not to open when a pressure difference equal to the first pressure drop is applied across the valve; and (2) to open when a pressure difference equal to the second pressure drop is applied across the valve.
In accordance with a second embodiment of the invention, a backhoe is provided that includes a vehicle, a hydraulic fluid pump, a hydraulic fluid tank fluidly coupled to and providing hydraulic fluid to the pump, a backhoe assembly coupled to the vehicle to swing with respect to the vehicle, at least one bi-directional dual-ported boom swing cylinder coupled to the backhoe assembly and the vehicle to swing the assembly, a bi-directional hydraulic control valve fluidly coupled to the pump and to the tank and to the at least one cylinder to regulate the flow rate and direction of the flow of actuating fluid to the at least one cylinder, first and second hydraulic conduits coupled to and between the control valve and the at least one cylinder, wherein the first and second hydraulic conduits are disposed to conduct the flow of hydraulic fluid to the at least one cylinder from the control valve and to the control valve from the at least one cylinder, and a swing damping circuit coupled to the first and second conduits for suppressing oscillation of the backhoe assembly, the circuit comprising a crossover valve in fluid communication with the first and second conduits to control the flow of hydraulic fluid between the first and second conduits and a hydraulic control circuit in communication with the crossover valve and configured to open the crossover valve in response to deceleration of the backhoe assembly with respect to the vehicle. The backhoe of claim 20, wherein the hydraulic control circuit may be responsive to a flow of fluid ejected from the cylinder by conversion of kinetic energy of the backhoe assembly. The crossover valve may be configured to open in response to the flow of fluid ejected from the cylinder by conversion of kinetic energy of the backhoe assembly. The hydraulic control circuit may include a first hydraulic signal line coupled to the crossover valve to apply a closing force to the crossover valve, and a second hydraulic signal line coupled to the crossover valve to apply an opening force to the crossover valve. Fluid pressure applied to the first hydraulic signal line may tend to close the crossover valve and fluid pressure applied to the second hydraulic signal line may tend to open the crossover valve. The first hydraulic signal line may be fluidly coupled to the first conduit when the fluid pressure in the first conduit is greater than the fluid pressure in the second conduit, and wherein the first hydraulic signal line may be also fluidly coupled to the second conduit when the fluid pressure in the second conduit is greater than the fluid pressure in the first conduit. The second hydraulic signal line may be fluidly coupled to the first conduit when the fluid pressure in the first conduit is greater than the fluid pressure in the second conduit and wherein the second hydraulic signal line may be also fluidly coupled to the second conduit when the fluid pressure in the second conduit is greater than the fluid pressure in the first conduit. The first hydraulic signal line may be configured to prevent hydraulic fluid that has entered the first hydraulic signal line from returning to the first and second conduits. The first hydraulic signal line may include at least one check valve configured to prevent fluid from the first hydraulic signal line from returning to the first and second conduits. The crossover valve may be configured (1) to open in response to a flow of fluid in the first conduit that is ejected from the cylinder by conversion of kinetic energy of the backhoe assembly, and (2) to open in response to a flow of fluid in the second conduit that is ejected from the cylinder by conversion of kinetic energy of the backhoe assembly. The hydraulic control circuit may be configured to apply the fluid ejected from the cylinder to the crossover valve to open the crossover valve to a position in which fluid can flow between the first and second conduits. The control valve may be configured to cause the deceleration of the backhoe assembly. The cylinder may include an internal piston that is movable inside the cylinder to define two regions: a first region coupled to the first hydraulic conduit to receive an actuating fluid flow from the first conduit and a second region coupled to the second hydraulic conduit to receive an actuating fluid flow from the second hydraulic conduit.
The foregoing and other features and advantages of the invention will become further apparent from the following detailed description of the presently preferred embodiment, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention rather than limiting, the scope of the invention being defined by the appended claims and equivalents thereof.